1. Field of the Invention
The present invention relates to a thermoplastic resin sheet having excellent thermal insulation property and a container being formed from the thermoplastic resin sheet.
2. Description of the Prior Art
Resin expanded materials are widely used as building/civil engineering materials, parts of air conditioning equipment, parts of refrigerating/freezing equipment, vehicle/marine vessel materials, container packaging materials and the like while making the most of their excellent thermal insulation property.
Furthermore, in order to improve the thermal insulation property of resin expanded materials, researches for improving cell structures of resin expanded materials have been made. For example, in Japanese Unexamined Patent Publication JP 11-245928-A (1999), it is reported that by making the maximum diameter dimension of cells in a polypropylene-based resin expanded sheet 500 xcexcm or less, the shape of cells is made roughly spherical, and further by setting the number of cells having roughly spherical shape within the range of 50% or more of the total number of cells for a unit area of the expanded sheet, it is possible to secure appropriate thermal insulation property for a food container obtained by forming the expanded sheet.
However, merely reducing the maximum diameter dimension can improve the thermal insulation property of the resin expanded materials within some restraint, so that it is difficult to obtain sufficient thermal insulation property.
In view of the above-described problem of the prior art, it is an object of the invention to provide a thermoplastic resin sheet having more excellent thermal insulation property and a container formed from the thermoplastic resin sheet.
The inventors of the present invention found that the above mentioned object can be achieved by providing a thermoplastic resin expanded layer having an inventive cell structure in the thermoplastic resin sheet, and reached the present invention.
To be more specific, the present invention provides a thermoplastic resin sheet having a thermoplastic resin expanded layer of which expansion ratio is in the range of 3 to 40 times, and cell wall density ratio is in the range of 2 to 20.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, and variations such as xe2x80x9ccomprisesxe2x80x9d and xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integer or step.